An alternative method for the determination of nitrate and nitrite : A microbial biosensor system based on cysteine-gold nanoparticle modified carbon paste electrode

In this thesis, a new microbial biosensor system based on AuNP / 3-MPA / S.cerevisiae modified carbon paste electrode was developed as a new and original alternative approach for the determination of nitrate and nitrite. In biosensor design, cysteine modified carbon paste electrode was prepared. Gold nanoparticle and 3-MPA were dropped onto the surface of the electrode, respectively. The resulting surface was then immersed in S.cerevisiae solution. The microbial biosensor system was designed for measurements of nitrite. However, repeatable standart graphics could not be obtained. Therefore, measurements for the determination of the other target molecule nitrate were performed. Nitrate measurements were carried out by differential pulse voltammetry method between (+0.2)V &( 0.9)V. The measurements were carried out using the linear relationship between the changes in oxidation peaks in the determined potential range of K4[Fe(CN)6] and nitrate concentration. In order to optimize the working conditions of the designed microbial biosensors, studies were carried out on temperature, pH and different buffers. In the studies carried out for characterization of microbial based biosensors, parameters such as determination of linear determination range, reproducibility, repeatability, substrate specificity,interference effect, stability and determination of nitrate in drinking water were determined. When the results obtained from the experimental studies were examined, the best working conditions were 50 mM, pH: 7.0 potassium phosphate buffer and 30ºC for the microbial based biosensor developed by the immobilization method. The linear determination range for microbial based biosensors and nitrate was found to be 100 µM.-750 µM. In the repeatability tests for the microbial based biosensor,the average value (n=10) for 400 µM nitrate concentration was found to be (x̄) = 398.03 µM, standard deviation (SD) = ± 1.33 µM and coefficient of variation % (C.L) = 0.3%. In addition, nitrate analysis was performed with microbial based biosensors in drinking sample water.